This invention relates to a drive mechanism for unfolding and folding, from a withdrawn position to an extended position and viceversa, external appendages of orbiting space vehicles, such as instruments, probes and other operative members. The peculiarity of the mechanism resides in its ability to perform the above described movements by means of purely mechanical actuators, not requiring electrical power for carrying out its tasks.
Unfolding devices for space applications are known which are based on spring-operated mechanisms, designed for one-shot operation. Once the vehicle had been launched to its final operational orbit, a radiosignal or other event was used to trigger a spring-retaining member to free the spring and allow the desired external probes to be unfolded. A big advantage of such one-shot devices was their simplicity and reliability, while their greatest limitation was--as is easily understandable--their inability to reverse the operation and/or to repeat the probe extension, though this limitation was usually no problem in the first days of orbiting systems.
However, with the onset of space transportation systems and the construction of large orbiting stations, the operational life of space systems--of increasing cost and size--has become longer, while maintenance and service in orbit has been introduced. Therefore, a need has arisen in some cases that the systems, before undergoing maintenance operations, be capable of autonomously resuming their launch configuration--by withdrawing their external appendages--so that they can be taken onboard interorbital transportation vehicles or the like.
The mechanical power for withdrawing said appendages, by moving them in a direction opposite to the unfolding movement, has been heretofore generally supplied by electric motors. This approach involves the installation of complex and bulky members, such as the motor itself, an electric power source such as a battery, and a system of switches to change the polarity in the motor supply, together with a decoding facility to allow different "unfolding" and "folding" signals to be recognized in the space vehicle. Moreover, such devices are inherently more prone to breakdown than the simple, mechanical "one-shot" mechanisms previously used.